"They were letting themselves get turned. It's down to the referee to spot it."
Maestri added that Barnes' failure to award a penalty try showed he had lost control.
"It was verging on nuclear warfare on the sidelines and the referee didn't react," he said.
France forwards coach Yannick Bru, however, was pleased his players did not let frustration get the better of them.
"I knew that Barnes, whom I've gotten to know over time, would not award a penalty try. But my players did not make any mistake," he said.
"We were more stubborn than Mr Barnes."
Wales were equally upset in the aftermath, however, accusing the French of making an unlawful substitution, which coach Rob Howley said brought the game's integrity into disrepute.
Starter Rabah Slimani was allowed back on as replacement prop Uini Atonio was taken off for a head injury assessment. Howley said he believes the substitution was planned.
"What happened in the last moments of that game shouldn't ever happen again," said Howley.
"One of the coaches had a word with their doctor and within a minute of that their tighthead went off. The evidence suggests that it's not in the integrity of our game."
100 minutes of rugby
It took a remarkable 20 minutes of injury time for France to score their winning try, with coach Guy Noves saying he had "never seen anything like that before".
Here is how the injury time period unfolded, via the Opta live commentary.
80th minute
We're into the final minute as France opt to go for the scrum from the penalty after there was no advantage coming. The home crowd are right behind their side now but the Welsh players are getting behind each other too knowing one good scrum could be enough.
81st minute
The scrum goes down and referee Barnes calls for a re-set and asks both sets of front rows to get higher. Atonio is going to have to leave the field for a HIA and is replaced by Slimani. Barnes doesn't seem convinced but the French doctor insists he does need a head assessment.
82nd minute
France get the ball out of the scrum and look to burrow their way over from close range through the forwards. Lopez then gets the ball out to Nakaitaci who is brought down just a metre short but France have another penalty.
83rd minute
Lee has been sent to the sin bin for the offence that lead to the penalty. Francis may well have to come back on here if France opt to go for a scrum from the penalty.
84th minute
Francis will have to come back on as France elect for a Scrum. No one seems to know who he's coming on for though and it's all becoming a bit farcical, but eventually Halfpenny makes his way off.
87th minute
Once again Barnes penalises Wales at the scrum, and once again France choose to have yet another scrum which then collpases, and will be re-set once more.
90th minute
The referee awards France another penalty but this time Picamoles takes a quick tap but is brought down just short of the line. France then shift the ball wide where Dulin knocks on, but referee Barnes brings play back for another penalty as Wales were not 10 metres, and there will be yet another scrum.
93rd minute
France finally get the ball out the back of the scrum and have another advantage coming their way as Webb is penalised for not releasing the ball carrier. Nothing comes of the attack though so France will have yet another penalty, and Barnes gives Warburton another warning.
94th minute
Lee's sin bin is over so he returns to the field along with Halfpenny, with Francis heading back to the bench for the second time.
95th minute
The referee is now checking with the TMO as there has been an allegation of a bite involving North in the middle of a tackle.
97th minute
There's no conclusive evidence of a bite so play will restart with yet another scrum from the France penalty.
99th minute
Another dominant French scrum results in another penalty, and despite a slight breakdown in communication between Barnes and the fourth official causing confusion, play will continue. France get another penalty and Barnes tells Wales that the next offence will result in another yellow card.
100th minute
TRY! France (Chouly) 18-18 Wales
100th minute
France get the ball away again and have another advantage coming as Dupont is brought down just two metre short by desperate last ditch defence., but they recycle the ball and Chouly forces his way over from close range.
100th minute
CONVERSION! France (Lopez) 20-18 Wales. Lopez kicks the conversion from the right-hand side of the posts to the win the game for France.
Full-time: France 20-18 Wales